The invention relates to a method as recited in the preamble of claim 1. Classical video recording allows trick modes such as fast forward and fast reverse. Trick modes have become more complex to implement for digital video that is compressed on the basis of groups of pictures (GOP), because uniform video intervals may correspond to data packet sequences of non-uniform lengths, depending on the information content of the video. U.S. Pat. No. 5,701,386 allows fast forward and fast reverse by providing each Group of Pictures with a GOP header and each sequence of GOPs with sequence headers both before its first GOP and also before its last GOP. Hereinafter, the term xe2x80x9cpicturexe2x80x9d will be used consistently. Depending on the actual video standard, the term xe2x80x9cpicturexe2x80x9d may include xe2x80x9cframexe2x80x9d as well as xe2x80x9cfieldxe2x80x9d. However, modern digital broadcast, in particular via satellite, uses Transport Streams (TS) according to system layer standard ISO/IEC 13818-1 for transmitting multi-channel audio and/or video. The video layer standard may be H262 or ISO/IEC 13818-2, the audio layer standard ISO/IEC 13818-3. These features are used inter alia for DVB and are intended for linear play without feedback from a decoder. Packets arrive at a receiver one by one and their assignment to a particular program is generally not known, before the packet itself will have arrived: indeed, assignment is through PSI-tables. For storage, one or more specific programs are selected from a received Transport Stream. This will necessitate either at storing time or at replay time the adapting of certain stream parameters for retaining a valid Transport Stream for replay.
Replay systems will generally support jumping over a selectable physical storage distance, but the probability of then hitting an entry point to the actually stored program is low. The finding of such entry points will necessitate repeated and time intensive searches, which may cause buffer underflow. It also becomes nearly impossible to replay the stream at an n times higher speed with n integer, as well as to land immediately on a video fragment that may be played independently. Therefore, if storage takes place on a dedicated apparatus, the locations of the entry points must be immediately known, either directly, or via pointers. The problem becomes more severe if a plurality of program must be stored.
In consequence, amongst other things, it is an object of the present invention to format stored video in such manner that various trick modes will become feasible for a Transport Stream environment, whilst maintaining the data handling facilities proper to this environment.
Now therefore, according to one of its aspects the invention is characterized according to the characterizing part of claim 1. The invention also relates to a method for replaying such recorded Transport Stream and to a device arranged for practising the invention. Further advantageous aspects of the invention are recited in dependent Claims.